1. Field of the Invention
The present invention relates to a method of estimating dc or low frequency target signals by a dynamical fluxgate sensor and a low-power magnetometer operating according to the method. In this mode of operation of a fluxgate magnetometer we take advantage of the inherent nonlinear (bistable) character of the core dynamics itself. Our approach, based on the passage time statistics of transitions to the stable steady states of the hysteresis loop, offers the possibility of using bias signals that have lower amplitude and frequency than those used in conventional fluxgate operation.
2. Description of Related Art
Fluxgate magnetometers are currently used as practical and convenient sensors for room temperature magnetic field measurements. Conventional fluxgate magneto-meters show a bistable dynamics (resulting from hysteresis in the ferromagnetic core) that is exploited in order to operate the device as a magnetic field detector. Standard operation is performed by applying a known very large-amplitude, time-periodic bias signal, to drive the fluxgate dynamics between the stable states. In the absence of the target signal, the underlying potential energy function is symmetric, and the response features contributions from only the odd harmonics of the bias signal. The presence of a target signal (usually taken to be dc or very low frequency) skews the hysteresis loop, resulting in the appearance of all the harmonics (or, combination tones if the target signal is time-periodic) of the bias signal frequency in the fluxgate response, usually quantified via an output power spectral density. The spectral amplitude at any tonal frequency in the power spectrum can then yield the strength of the target signal, although in most applications the second harmonic of the bias signal is used since its spectral amplitude is proportional to the target signal amplitude as well as the bias frequency.
Conventional fluxgate readout schemes are limited by internal noise. Specifically, a large-amplitude, high frequency bias signal cant amounts of Barkhausen noise, and also: generate a strong 1/f component that degrades the sensor response. In addition, generating a bias signal of large amplitude and frequency requires a large power-source that severely limits the practical applicability of the sensor.